This invention relates generally to a poultry immersion scalding system and process in which poultry is conveyed in an open immersion tank containing scalding liquid as the conveyor moves the poultry while hanging by the legs. More particularly, the poultry is conveyed in one direction through the tank, and the scalding liquid is emptied from the tank and returned to flow in a direction opposite the poultry conveying direction, the liquid thus recirculated being filtered and additional liquid being added and heated before being returned to the immersion tank.
For a typical start-up operation of immersion scalders, the immersion tank is filled with clean water and heated to the desired scald temperature. The water can be heated by live steam injection, by steam passing through heat exchange plates in the immersion tank or by hot air and steam injection into the scald water. During operation approximately one quart of clean tap water is added for every bird moving through the immersion tank. The make-up water is usually at ground temperature, i.e., 65.degree. F. to 70.degree. F. The birds pass through the scald (immersion) tank for 8-16 hours per day. Counting work breaks the water can be 18 hours old when the last bird exits the scalder.
The fresh make-up water of about one quart per bird helps maintain the water level in the immersion tank as the birds carry water out in their feathers. Also, the U.S.D.A. normally requires an overflow of water from the scald tank. This provides some dilution of the contaminated water but has very little effect. The cold add water is sometimes added to the tank at a concentrated location, but is normally added through a perforated pipe extending along the scalder for dissapating the cold make-up water so as not to create cold spots in the tank which could defeat the purpose of the scalder.
The flow of water in a scalder allows water to be mixed during conveyance of the poultry along adjacent conveyor runs as the birds travel in opposite directions relative to one another. The flow of water is not directed in a controlled path nor in any purposeful direction.
The typical immersion scalder presents considerable cross-contamination problems. A bird having very little bacteria will pick up bacteria in the water from birds that have passed before it. In many cases bacteria types may be introduced into the bird that it does not have until it is immersed in the scalder.
As well known, a scalder is utilized as part of a poultry processing operation so as to heat the skin of the bird to loosen the feathers allowing the feathers to be plucked at a station after the birds leave the scald tank. The bird's feathers act as insulation preventing heat from reaching the skin.
In immersion scalding the birds are carried by an overhead conveyor hanging by the feet and are immersed in a hot bath of water. The water is heated and agitated by air injection in the bottom of the scalder or by pumps moving large volumes of water that flow over the birds. During the scalding Process the skin and feathers are heated by the heat transfer of hot water (124.degree. to 142.degree. F.) into the bird.
Non-immersion scalders are also known which utilize live steam injection for heating the skin of the bird to loosen the feathers for subsequent plucking. However, since the scalder tank is open significant steam blow-by from the top of the scalder is experienced with such live steam injection scalders. This steam reaches the surface of the scald water before it completely dissipates into the water.
Factors that contribute to scalding are temperature and time. For a hard scald, higher water temperature could mean less time in the scalder for the heat transfer required to loosen the feathers. This is limited, however, because at temperatures as high as 142.degree. F. the bird may cook. For this reason it is not possible for scald water to be heated sufficiently high to kill many types of bacteria.
Also it takes more time to soft scald the bird than it does for a hard scald. Soft scald is used when the preferred end product is a yellow bird. The outer layer of skin which carries the yellow color is easily overheated and will if overheated be removed from the bird in the pickers along with the feathers. For this reason the temperature is lower than hard scald, although bacteria of many types cannot be killed by the low temperature of the water.
Other factors contributing to temperature and time are bird health, rigor mortis, the Ph of the water, the poultry breed, the weather, the type Of immersion scalder, the picking system, the type of kill cut and bleed time.
The soft scald temperature of broiler chickens is about 124.degree. to 130.degree. F., with an average of 127.degree. to 128.degree. F. The hard scald temperature of broiler chickens is between about 130.degree. to 140.degree. F. Turkeys are always hard scalded at a temperature between 137.degree. to 140.degree. F. And, the make-up water for immersion scalders usually amounts to one quart per bird for chickens and one half gallon per bird for turkeys.